1. Field of the Invention
This invention relates to safety devices for bombs, or vessels for compressed gases, which enable the operator to open and close the valve of the bomb containing a poisonous, or an inflamable or ignitable gas without incurring danger.
2. Description of the Prior Art
A poisonous, or an inflammable or ignitable gas contained in a bomb, i.e., a cylindrical vessel for compressed gases with a gas flow regulating valve, is often used in the industry. For example, arsines, phosphines, silanes, and diborane, which are extremely poisonous, and inflammable or ignitable, are used in the production of semiconductor devices. Thus, leakage of small quantity of these gases may entail grave results: the opening and closing operation of the valve of the bomb containing these gases is accomplished by great dangers.
In former years, safety devices for the bombs for detecting the presence of leaking gas have already been proposed; to date, however, none which enables the operator to open and close the valve of the bomb safely.
Japanese laid-open utility model application 59-90698, for example, teaches a protector cap for the vessels of poisonous gases for ensuring safety during the transportation of the bombs. The protector cap comprises a cover having the form of an inverted cup which is attached to the top of the bomb, a detector tube disposed at the ceiling of the cover which comprises a detector agent observable from without, an antidotal agent disposed in the cover, and an antidotal cylinder disposed in the cover and having a gas introducing port and a gas exhausting port which communicates with the exterior.
The protector cap taught in this Japanese utility model application, however, has following disadvantages. First, it is designed solely to detect and treat the leaking gas during the transportation, and no regard is paid to the safety during the opening and closing operation of the valve which becomes necessary when the gas is utilized in a factory. Second, the detection of the leaking as is effected only qualitatively, not quantitatively. Third, as the time point at which the antidotal agent loses the antidotal efficiency is not readily recognizable, there is a danger that the operator keeps on using the antidotal agent which has already lost its effects. Fourth, until the pressure of the leaking gas in the cover reaches a certain level, the leaking gas does not flow into the antidotal cylinder. Fifth, when the leaking late of the gas is high, the antidotal agent may not be enough to counteract the poisonous gas. Sixth, the exterior air may flow into the antidotal cylinder through the gas exhausting port which is open to the exterior space, so that if the bomb contains an ignitable gas, the danger that the leaking gas catch fire is not completely eliminated.
Japanese utility model application 61-96352, on the other hand, teaches an oxygen detecting cap for oxygen bombs, which comprises a main body of the cap hermetically fitted around the oxygen extracting portion of the oxygen bomb, in which a deoxygenating agent and an oxygen detecting agent are disposed.
The cap taught by this Japanese utility model application suffers following disadvantages. First, it is designed solely to detect and treat the leaking gas during transportation or storage time thereof, and no regard is paid to the safety of the opening and closing operation of the valve during the time in which the gas is utilized. Second the detection of the leaking gas is effected only qualitatively and not quantitatively. Third, as the leakage of the gas is detected by the changing color of the detector agent, a small quantity of leaking gas may be overlooked. Fourth, although the oxygen gas leaking into the main body of the cap is gradually removed by the deoxygenating agent, the leaking oxygen gas remaining in the main body of the cap may be diffused to the exterior when the main body of the cap is removed from the bomb. Thus, the cap is not applicable to vessels containing gases utilized in the production of semiconductor devices, which are highly harmful to human body even in small quantity or are ignitable when they come into contact with air.
Further, Japanese laid-open patent application 55-18971 teaches a detector device for radioactive leaking gas, which comprises a retrieving hood covering the whole storage vessel sealing a radioactive substance therein, and a sampling pipe which supplies the radioactive leaking gas retrieved by the hood to a detector.
The detector device taught by this Japanese patent application suffers the disadvantage that, although it is possible to recognize which vessel is leaking during storage time, no means is provided for the safety when the gas in the vessel is used. The device also suffers the disadvantage that it is cumbersome and difficult to handle because the retrieving hood covers the whole storage vessel.
Thus, conventional safety devices for the bombs are only effective to detect and counteract the leaking gas during transportation or storage time of the bomb; the opening and closing of the valve of the bomb cannot be effected without removing the protector cap enclosing the valve of the bomb. Therefore, in cases in which the gas contained in the bomb is poisonous, or inflamable of ignitable great danger may accompany the opening and closing operation of the valve of the bomb. Namely, when the protector cap is removed from the top of the bomb to operate the valve when the gas in the bomb is to be used, the leaking gas which may be present in the protector cap is diffused to the exterior space. Further, as no safety means is provided during the time when the gas is used, the valve may fail on repeated opening and closing operations after the cap is removed, so that the gas is leaked and diffused therefrom. In both these cases, the diffusion of the poisonous, or inflammable or ignitable gas may harm the operators or cause a fire.